Substrate of circuit board

ABSTRACT

An object is to provide a metal-clad laminated board applicable for a printed wiring board capable of readily dissipating heat and superior in thermal conduction, and further, the printed wiring board substrate overlaid with a lead frame having the same characteristics as the metal-clad laminated board. To attain the aforesaid object, the printed wiring board of the invention has the carbon-base substrate overlaid with metal foil or lead frame through an insulating bonding layer. Thus, in a case of using the metal foil, the printed wiring board is formed in a metal-clad laminated board, and in a case of using the lead frame, the printed wiring board is formed in a lead frame laminated board.

TECHNICAL FIELD

This invention relates to a substrate for printed wiring boards. Moreparticularly this invention relates to a metal-laminated board orsubstrate for wiring boards, which is overlaid with a lead frame. Stillmore particularly this invention relates to he aforesaid substrates madeof carbonaceous material and having excellent heat conductivity.

BACKGROUND ART

Conventionally, a printed circuit board forming printed wiring thereonhas been generally produced by use of photolithography, namely drawing awiring pattern on the so-called metal-clad laminated board made by covera substrate with metal foil such as copper foil by using photo resistand etching the desired wiring pattern thereon. The printed circuitboards thus produced have been used as wiring substrates for variouselectrical and electronic apparatuses. Forming of the printed circuitboard using the substrate laminated with metal is suited to amicroscopic processing for forming a very small wiring pattern withease. Thus, this microscopic technique makes it possible to produce aprinted circuit board having very small wiring. In general, a substratemade of synthetic resin such as phenol plastic has been widely used asthe metal-clad laminated board, by way of example.

Further, in general wiring board substrates overlaid with the so-calledlead frame punched out from a metal plate such as of copper have beenapplied to various electric and electronic apparatuses. The wiring boardsubstrate overlaid with the aforesaid lead frame (hereinafter, simplyreferred to as “lead-frame laminated substrate) is inferior inproductivity to a metal-clad electric wiring boards Thus, the lead-framelaminated substrate is inferior in fine machinability in forming wiringpatterns, but easy to manufacture, so that the wiring board can beproduced at a low cost. Besides, the lead frame made as thick asrequired for the purpose can advantageously withstand high electriccurrent, consequently to produce the wiring board having low electricalresistance loss with ease. The lead-frame laminated substrate and themetal-clad electric wiring board are respectively used for each purpose,taking into consideration various conditions such as the merit, demeritand object required for the electric wiring board and various conditionsrequired for electric or electronic apparatus to which the electricwiring board is applied. A lead-frame laminated substrate made from aplastic board such as of phenol plastic has been widely used so far.

In general, a circuit formed on the electric wiring board or lead-framelaminated substrate generates heat has danger of causing unexpectedtrouble due to intense heat accumulated, though varying with the type ofthe components for forming the circuit. Accordingly, the electric wiringboard is required to release the heat quickly. However, both theelectric wiring board made from the metal-clad laminated substrate ofthe conventional plastic board and the lead-frame laminated substrateusing the conventional plastic board entail are disadvantageous in thatthey are inferior in heat conductivity, and therefore, cannot meet thedemand for releasing the heat.

An object of the present invention is to provide a metal-clad laminatedboard having excellent heat conductivity so as to form a printed circuitboard capable of releasing generated heat quickly and a lead-framelaminated substrate having excellent heat conductivity so that the heatgenerated can be released quickly.

DESCRIPTION OF THE INVENTION

The inventor of the invention completed this invention upon close anddiligent investigation in order to attain the object described above.According to the invention, there is provided a metal-clad laminatedsubstrate or lead-frame laminated board for forming a printed circuitboard, which is produced by using a carbon-base substrate made ofcarbonaceous material having an excellent heat conductivity and aninsulating bonding layer for steadily joining metal-foil or lead frameto the carbon-base substrate.

Namely, in order to attain the aforementioned object of the presentinvention, there is provided a metal-plated laminated board for a wiringboard characterized in that the carbon-base substrate is overlaid withthe metal foil or lead frame through an insulating bonding layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic section showing one example of a metal-cladlaminated board of one embodiment of a printed circuit board accordingto the invention.

FIG. 2 is a diagrammatic section showing another example of a lead-framelaminated board of one embodiment of the printed circuit board accordingto the invention.

FIG. 3 is a diagrammatic section showing still another example of thelead-frame laminated board of one embodiment of a printed circuit boardaccording to the invention.

FIG. 4 is a diagrammatic section showing yet another example of thelead-frame laminated board of one embodiment of a printed circuit boardaccording to the invention.

FIG. 5 is a diagrammatic section showing another example of themetal-clad laminated board of one embodiment of a printed circuit boardaccording to the invention.

FIG. 6 is a diagrammatic section showing still another example of themetal-clad laminated board of one embodiment of a printed circuit boardaccording to the invention.

FIG. 7 is a diagrammatic section showing yet another example of themetal-clad laminated board of one embodiment of a printed circuit boardaccording to the invention.

FIG. 8 is a diagrammatic section showing further example of themetal-clad laminated board of one embodiment of a printed circuit boardaccording to the invention.

FIG. 9 is a diagrammatic section showing the other example of themetal-clad laminated board of one embodiment of a printed circuit boardaccording to the invention.

FIG. 10 is a diagrammatic section showing the other example of themetal-clad laminated board of one embodiment of a printed circuit boardaccording to the invention.

FIG. 11 is a diagrammatic section showing the other example of themetal-clad laminated board of one embodiment of a printed circuit boardaccording to the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The substrate for wiring boards is made in a form of a metal-cladlaminated board when overlaid with metal foil or a lead-frame laminatedboard when overlaid with a lead frame. The carbon-base substrate of thewiring substrate of the invention is generally made of a plate ofcarbonaceous material such as carbon fiber reinforced composite havingcarbon matrix of carbon fiber reinforcer or isotropy high density carbonmaterial In a case that the carbon-base substrate is too thin, thestrength thereof is decreased. In a case that the substrate is madethick, it becomes heavy and expensive. Therefore, the thickness of thesubstrate must be determined taking this conditions into consideration,but it is generally desirable to determine the thickness of thesubstrate on the order of 3 to 5 mm.

The carbon fiber reinforced composite used for the carbon-base substratemay be arbitrarily selected from various carbon fiber reinforcedcomposites conventionally known. Generally, the carbon fiber reinforcedcomposites are featured according to the orientation of carbon fibers,i.e. sorted into a first-order oriented type having the carbon fiberfabrics woven in one direction, a second-order oriented type havingcarbon fiber fabrics like a plain weave, diagonal weave or satin weave,a third-order oriented type having steric carbon fiber fabrics. Theremay also be used felt or short fiber fabrics. Various fabrics having anycarbon fiber orientation may be arbitrarily applied to the presentinvention. The carbon fiber reinforced composite is generally producedby impregnating carbon fiber polymer having the carbon fiber orientationas noted above with thermosetting resin such as phenol resin or pitchmatrix material such as of petroleum pitch to prepare pre-pregs,laminating the pre-pregs one on top of the other as required to make amatrix heating the matrix of laminated pre-pregs under pressure toharden the matrix, and baking the matrix at high temperature in inertatmosphere to carbonize the matrix. Generally, the carbon fiberreinforced composite formed of short fiber fabrics is produced byforming the matrix containing short carbon fibers in a desired shape,heating it under pressure, baking the matrix in inert atmosphere tocarbonize the matrix. The carbon fiber reinforced composite for thecarbon-base substrate may be produced by molding the matrix into adesired shape with desired thickness or cutting a carbon fiber matrixlump into the desired shape. The carbon fiber and carbon matrix forpreparing various types of carbon fiber reinforced composites may begraphitized.

Of the carbon fiber reinforced composites described above, it ispreferable to prepare a plate-like carbon matrix having carbon fibersoriented in its thickness direction, which is produced in such a mannerthat the carbon fiber reinforced composite having the first-orderorientation of carbon fibers oriented in one direction is cut in thedirection perpendicular to the orientation of the carbon fibers. Thecarbon fiber reinforced composite can desirably be used as thecarbon-base substrate, since it excels in heat conductivity in thethickness direction. Cutting of the carbon fiber reinforced compositefrom the aforesaid carbon fiber matrix lump can be performed by using aconventionally known cutting device such as a wire saw and a rotarydiamond saw.

One embodiment of the metal-clad laminated board for the electric wiringboard according to the present invention, in which the plate-like carbonfiber reinforced composite is used as the carbon-base substrate, isdiagrammatically illustrated in FIG. 1. In the metal-clad laminatedboard in FIG. 1, insulating bonding layers 2 containing carbon fibers 1b oriented in the thickness direction of a carbon matrix 1 a. The metalfoil layer of the metal-clad laminated board may lie on both sides ofthe carbon-base substrate as shown in FIG. 1 or either side of thecarbon-base substrate. One example of the plate-like carbon-basesubstrate having a lead-frame laminated board according to the presentinvention is diagrammatically illustrated in FIGS. 2 through 4. In thelead-frame laminated board in FIGS. 2 to 4, the carbon fibers 1 b in thecarbon matrix 1 a are oriented in the thickness direction of the matrix,and insulating bonding layers 2 and lead frame layers 4 are placed onone of the surfaces of the carbon-base substrate 1. In the electricwiring board formed as the lead-frame laminated board according to theinvention, the lead frame layers 4 may be placed on one of the surfacesof the carbon-base board 1 as shown in FIG. 2 to 4 or on both surfacesthereof. The insulating bonding layers 2 may be placed between each leadframe layer 4 and the carbon-base substrate 1 as shown in FIG. 2, oroverlaid on the whole surface of the carbon-base substrate 1 as shown inFIG. 3. The lead frame layers 4 may be embedded in the surface portionof the insulating bonding layer 2 so as to make the surface of theentire board flat as shown in FIG. 4.

Also in the case of using isotropy high density carbon material as theaforesaid carbon-base substrate, it may be arbitrarily selected from avariety of isotropy high density carbon materials which have beengenerally known. The isotropy high density carbon material is generallyproduced by molding and sintering minute particles of sinterablegraphite precursor such as of raw coke and mesocarbon micro beads underpressure or a mixture of minute graphite particles or carbon whiskerpowder and a binder of minute particles of graphite precursor. Theisotropy high density carbon material for the carbon-base board may beformed in a plate shape or like a lump so as to be ultimately made flatby cutting. The aforesaid isotropy high density carbon materials may begraphitized.

The carbon fiber reinforced composite and isotropy high density carbonmaterial having fine pores formed in the producing process therefore areporous. These porous materials are impregnated with inorganic coatingagent or metal in order not to be porous, consequently to more increasetheir heat conductivity. Accordingly, the carbonaceous material as notedabove may be used as the carbon-base substrate by being impregnated withthe inorganic coating agent or metal to fill the fine pores in thecarbon material. This treatment is desirable from the viewpoint of theheat conductivity of the substrate.

The inorganic coating agent with which the aforesaid carbonaceousmaterial is impregnated may be selected from various liquid inorganiccoating agents capable of saturating to the fine pores in thecarbon-base substrate and solidifying after saturating into thecarbon-base substrate, consequently to form a non-porous solid inorganiclayer in the carbon-base substrate. By way of example, there may beused, as the coating agent, inorganic silicon-containing polymer fromwhich a ceramic solid is derived by crosslinking reaction at roomtemperature or high temperature, cement such as alumina cement, andinorganic binder containing water-glass or the like. These inorganiccoating agents may be diluted with an organic solvent in order toincrease the impregnating ability thereof To be more specific, as theaforementioned inorganic coating agent, there may be generally usedHEATLESS GLASS GA series (trade name of Homer Technology Co. Ltd.) whichis silicon-containing polymer, Tonen Polysilazane (trade name of TonenPetrochemical Co. Ltd.) which belongs to polysilazanes, Redproof MR-100series (trade name of Heat System Research & Industry Inc.) which is aninorganic binder, and so on.

Infiltration of the inorganic coating agent into fine pores in thecarbon-base substrate can be carried out by applying the inorganiccoating agent to the carbon-base substrate with a brush, saturating thecarbon-base substrate in the inorganic coating agent, forcibly injectingthe inorganic coating agent into the carbon-base substrate underpressure, or causing the carbon-base substrate to be spontaneouslyimpregnated with the inorganic coating agent in a vacuum, by way ofexample. As a result, the inorganic coating agent saturating into thecarbon-base substrate solidifies. The solidifying condition of theinorganic coating agent varies with, for example, the sort or type ofthe inorganic coating agent. In a case of using HEATLES GLASS as theinorganic coating agent, it is desirable to heat it at about 130° C. for60 minutes, in general.

As the aforementioned metal to saturating into the carbon-basesubstrate, there may be preferably used aluminum, copper or a mixturethereof. Infiltration of the metal into fine pores in the carbon-basesubstrate can be carried out by saturating molten metal such as aluminumand copper thereinto under high pressure. As the carbon-base substrateimpregnated with aluminum, there are enumerated CC-MA (trade name ofSentan Zairyo, as which C/C composite base having carbon fibers orientedin first order is designated), and C-MA (trade name of Sentan Zairyo, aswhich isotropy high density carbon material is designated) and so on. Asthe carbon-base substrate impregnated with copper, there are enumeratedMB-18 (trade name of Mebius AT, as which C/C composite base havingcarbon fibers oriented in first order is designated) and so on.

The metal foil applied to the metal-clad laminated board of the electricwiring board according to the invention may be selected from a varietyof metal foil materials conventionally known as foil applicable forproducing the metal-clad laminated board. In general, copper foil ornickel foil is preferably used for this purpose. The metal foil may bejoined to one or both of the surfaces of the carbon-base substrate. Thelead frame applied to the lead-frame laminated substrate of the electricwiring board of the invention may be selected from various types of leadframes conventionally known as the lead frame for producing elasticwiring boards, which are produced by punching out a desired wiringpattern or in other suitable methods. In general, a lead frame of copperor nickel is preferably used. The lead frame may be joined to one orboth of the surfaces of the carbon-base substrate.

Next, the insulating bonding layer will be described The insulatingbonding layer through which the aforementioned metal foil or lead frameis joined with the aforementioned carbon-base substrate is preferablymade thin and excellent in insulating properties and bonding property soas to firmly unite the metal foil or lead frame to the carbon-basesubstrate. However, it is common knowledge that an ordinary adhesiveagent is hard to merge into the carbon-base substrate and unlikely toproduce sufficient bonding strength relative to the carbon-basesubstrate. To solve this problem, the insulating bonding layer in thepresent invention may be formed of (i) a structure of polyimide coatingmembrane on the carbon-base substrate and an bonding layer placed on thepolyimide coating membrane, (ii) a structure of polyimide-vaporizedpolymer layer on the carbon-base substrate and an bonding layer placedon the polyimide-vaporized polymer layer, (iii) a structure in which apolyimide layer having bonding property is placed on the carbon-basesubstrate, (iv) a structure of a metal-clad layer on the carbon-basesubstrate and an bonding layer placed on the metal-clad layer, or (v) astructure of a primer layer on the carbon-base substrate and an bondinglayer placed on the primer layer. With any of these structures for theinsulating bonding layer, the carbon-base substrate in the invention canbe firmly bonded to the metal foil or lead frame while ensuringsufficient insulating and bonding properties, so as to be put intopractical use. That is, by previously forming a primary layer such asthe aforementioned polyimide coat and polyimide-vapored polymer layer orselecting the polyimide layer having bonding property as the insulatingbonding layer, the metal foil or lead frame can be strongly bonded tothe carbon-base substrate with sufficient strength in practicalapplication. In general, the insulating bonding layer is preferably madethin so as not to impede its heat conductivity in the perpendiculardirection of the electric wiring board.

First, the item (i) describe above will be explained. The polyimidelayer on the insulating bonding layer noted in the item (i) can beformed by, for example, applying any of various polyimide coatingconventionally known to the carbon-base substrate. The polyimide coatingmay be prepared by dissolving either polyimide acid or polyimide resinin a solvent, but the latter can be practically used so that a coatinghaving relatively excellent heat conductivity can be formed, since ithas no need for a process of dehydrating by heating. By way of example,RIKACOAT (trade name of New Japan Chemical Co. Ltd) and UPIREX-S (tradename of Ube Industries, Ltd.) may be suitably used for this purpose. Tothe polyimide coating, various additives may be added in order toincrease the insulating properties and stability of the coating. In theaforesaid manner, the polyimide coating formed on the carbon-basesubstrate is overlaid with the metal foil or lead frame through theagency of the bonding layer, and these layers are firmly bonded togetherby heating or under pressure at room temperature. As a result, therequired electric wiring board integrally bonded with the metal foil orlead frame can be formed. The aforesaid bonding conditions may bedetermined according to the type of the polyimide coating. Theembodiment of the metal-clad laminated board using the insulatingbonding layer featured by the item (i) noted above is diagrammaticallyillustrated in FIG. 5 by way of example. In the embodiment of themetal-clad laminated substrate of FIG. 5, the both surfaces of thecarbon-base substrate 21 are respectively coated with the insulatingbonding layer 22 composed of the polyimide coating 22 a and the bondinglayer 22 b and the metal foil layer 23 in order. Thus, the electricwiring board in the form of the metal-clad laminated board can beproduced.

As the polyimide coating membrane to be formed on the insulating bondinglayer, electrode position polyimide coating may be suitably used. Theelectrode position polyimide coating membrane may be selected fromvarious types of electrode position polyimide coatings, in which itsresin component is polyimide and a medium is a cation solution. Theelectrode position polyimide coating membrane may contain any of variousadditives in order to improve its insulation property and stability. Theelectrode position polyimide coating membrane can be formed on thecarbon-base substrate by an electrode position coating method. As theelectrode position coating method to be applied to the invention, therehave been so far known various methods. Onto the electrode positionpolyimide coating membrane formed by the electrode position coatingmethod, the metal foil or lead frame is bonded through the bonding layerby heating or under pressure, so that the required electric wiring boardhaving the carbon-base substrate firmly united with the metal foil orlead frame can be obtained. The aforementioned bonding conditions may bedetermined according to the type of the electrode position polyimidecoating applied to the electric wiring board The embodiment of themetal-clad laminated board using the electrode position polyimidecoating featured by the item (i) noted above is diagrammaticallyillustrated in FIG. 6 by way of example. In the embodiment of themetal-clad laminated board shown in FIG. 6, the both surfaces of thecarbon-base substrate 31 are respectively coated with the insulatingbonding layer 32 composed of the polyimide coating 32 a and the bondinglayer 32 b and the metal foil layer 33 in order. Thus, the desiredelectric wiring board can be produced.

Next, the item (ii) described above will be explained. Thepolyimide-vaporized polymer layer on the insulating bonding layer notedin the item (i) can be formed by a known vaporization polymerizingmethod, for example. That is, an hydride such as pyromelliticdianhydnde, biphenyl tetracarboxylic dianhydride and benzophenonetetracarboxylic dianhydride and armatic diamine such as oxydiniline,paraphenylene diaiine and benzophenone diamine are vaporized together onthe carbon-base substrate and heated to make an imide layer. Thepolyimide-vaporized polymer layer can easily be controlled in itsthickness and formed in an exactly flat membrane. Thus, the carbon-basesubstrate and the metal foil or lead frame can be firmly united withsufficient insulating properties. The embodiment of the metal-cladlaminated board using the insulating bonding layer featured by the item(ii) noted above is diagrammatically illustrated in FIG. 7 by way ofexample. In the embodiment of the metal-clad laminated board shown inFIG. 7, the both surfaces of the carbon-base substrate 34 arerespectively coated with the insulating bonding layer 35 composed of thepolyimide-vaporized polymer layer 35 a and the bonding layer 35 b andthe metal foil layer 35 in order. Thus, the desired elastic wiring boardcan be produced.

Next, the item (iii) described above will be explained. The process formaking the insulating bonding layer having a multi-layer constructionconstituted by the polyimide coating layer or polyimide-vaporizedpolymer layer as touched upon above in connection with the items (i) and(ii) noted above is complicated, but desirable in order to conserve thesufficient bonding strength. However, the process of the item (iii)becomes relatively simple. The polyimide in this process serves as thebonding layer in the items (i) and (ii). The polyimide layer having sucha bonding function may be selected from a known polyimide bonding agentsuch as UPITITE (trade name of Ube Industries, Ltd) and KAPTON (tradename of DuPont-Toray Co. Ltd.). Thus, the required electric wiring boardwith the polyimide layer having the aforementioned bonding property canbe produced by bonding the metal foil or lead frame onto the carbon-basesubstrate in accordance with the type of the polyimide bonding agentapplied thereto (which type is determined with the thermosettingproperty, thermal plasticity of the polyimide bonding agent, and formsuch as of a film type or a solution type). In a case of using the filmtype thermoplastic polyimide bonding agent, the film type bonding agentis placed between the metal foil or lead frame and the carbon-basesubstrate and then heated under pressure, thereby to firmly unite themetal foil or lead frame and the carbon-base substrate. The embodimentof the metal-clad laminated board using the insulating bonding layerfeatured by the item (iii) noted above is diagrammatically illustratedin FIG. 8 by way of example. In the embodiment of the metal-cladlaminated board shown in FIG. 8, the both surfaces of the carbon-basesubstrate 37 are respectively coated with the polyimide layer 38 havingthe bonding property and the insulating bonding or metal foil layer 39in order. Thus, the desired electric wiring board can be produced

The polyimide bonding agent noted in the item (iii) above may beoverlaid on the polyimide coating membrane noted in the item (i) aboveor the polyimide-vaporized polymer layer noted in the item (ii) above.That is, upon forming the polyimide coating membrane (including theelectrode position polyimide coating membrane) or polyimide-vaporizedpolymer layer on the carbon-base substrate, the metal fail or lead frameis placed on the polyimide coating membrane or polyimide-vaporizedpolymer layer through the polyimide bonding agent noted in the item(iii). Thus, the desired electric wiring board can be produced.

In a case of using the film type thermoplastic polyimide bonding agentas the bonding layer to be laid on the polyimide coating membrane on thecarbon-base substrate, the coating component of the polyimide coatingmembrane soaks into the pores in the surface of the carbon-basesubstrate, thereby to plug up the pores in the process of bonding themetal foil or lead frame to the carbon-base substrate under pressure. Asa result, the heat conductivity of the wiring board can be increased,and the insulating properties can be ensured owing to the film typethermoplastic polyimide bonding agent by which the carbon-base substrateis securely isolated from the metal foil or lead frame.

Next, the item (iv) described above will be explained. The insulatingbonding layer in the term (iv) is plated with metal by an electrolessplating or electric plating method well-known conventionally. As themetal to be plated on the insulating bonding layer, there may be usedcopper, nickel and so on. The metal plating layer is overlaid with themetal foil or lead frame through the bonding layer. Then, a laminatedboard thus obtained is heated or pressed at room temperature. Thus, therequired elect wiring board in which the metal foil or lead frame isfirmly united with the carbon-base substrate can be produced.Incidentally, the bonding layer on the metal plating layer necessitatesinsulating properties. The metal plating layer in the term (iv)functions as a primer and satisfactorily meet the requirements for thebonding ability for the carbon-base substrate. The embodiment of themetal-clad laminated board using the insulating bonding layer featuredby the item (iv) noted above is diagrammatically illustrated in FIG. 9by way of example. In the embodiment of the metal-clad laminated boardshown in FIG. 9, the both surfaces of the carbon-base substrate 41 arerespectively coated with the polyimide layer 42 formed of the metalplating layer 42 a and the bonding layer 42 b and the metal foil layer43 in order. Thus, the required electric wiring board can be produced.

As the bonding agent used in the embodiments of the terms (i), (ii) and(iv), there may be suitably used epoxy resin adhesive, silicon adhesiveand the like, other than the aforementioned polyimide bonding agent. Asthe silicon adhesive, there may be used, for instance, KE1800T (tradename of Shin-Etsu Silicones Co. Ltd.) and TES-3260 (trade name of GETbshiba Silicones Co. Ltd.) Also, the inorganic coating agent such asHEATLESS GLASS GA touched upon above may be used as the bonding agent asnoted above. The bonding agent is applied to the polyimide coatingmembrane, polyimide-vaporized polymer layer or metal plating layerhereinafter, referred to as an “undercoat”), thereby to form the bondinglayer. The bonding agent may be applied to the undercoat by aconventionally known coating method. The formation of the bonding layeron the undercoat may be performed by (a) applying the bonding agent ontothe undercoat laid on the carbon-base substrate and placing the metalfoil or lead frame on the bonding agent, (b) first applying the bondingagent to one surface of the metal foil or lead frame and then placingthe metal foil or lead frame on the undercoat laid on the carbon-basesubstrate with the bonding layer of the bonding agent coming intocontact with the undercoat, (c) applying the bonding agent to both theundercoat on the carbon-base substrate and one surface of the metal foilor lead frame, and uniting together the carbon-base substrate and themetal foil or lead frame with the bonding agent layers on thecarbon-base substrate and the metal foil or lead frame coming intocontact with each other, or (d) laminating the film-like bonding agentin its incomplete hardened state and the metal foil or lead frame on theundercoat of the carbon-base substrate. In placing the metal foil orlead frame on the carbon-base substrate, it is desirable to press theselayers by using a roll press, platen press or the like in order toclosely unite the layers without remaining air in between the layers. Inbonding the layers, a primer as described in detail later may optionallybe applied to the undercoat and the metal foil or lead frame with abrush.

The drying or heating condition of the aforementioned bonding agent maybe arbitrarily determined in accordance with the type of the bondingagent applied. In a case of using TES-3260 (trade name of GE ToshibaSilicones Co. Ltd.) as the bonding agent, it is preferable to heat it at150° C. for 60 minutes under pressure.

Next, the item (v) described above will be explained In forming theinsulating bonding layer in the term (v), there may be used, as a primerfor forming a primer layer, PRIMER-A (trade name), PRIMER-X (trade name)and PRIMER-Y (trade name), which are put on the market by Dow-CorningToray Silicone Co. Ltd. To be concrete, as the elastomer bonding layerapplied to the primer layer, which requires insulating properties, theremay be suitably used SOTEFA-70 (trade name as which silicone elastomerbonding agent is called) of Dow-Corning Toray Silicone Co. Ltd.Incidentally, this elastomer bonding agent may be used as the bondingagent formed on the insulating bonding agent in the aforementioned items(i), (ii) and (iv). This elastomer bonding agent may contain agranulated heat conductive filler such as SiN, SiC and Al₂O₃, accordingto demand. The aforesaid heat conductive filler may be added to thebonding layer in the insulating bonding layer of the items (i), (ii) and(iv) described above and the polyimide layer having bonding ability inthe item (iii) described above. The elastomer bonding layer laid on theprimer layer is dried or hardened by heat, thereby to firmly unite themetal foil or lead frame onto the carbon-base substrate. As a result,the required electric wiring board can be produced. The processingconditions for drying or hardening the elastomer bonding layer by heatare determined in accordance with the type of the elastomer bondingagent applied thereto. The embodiment of the metal-clad laminated boardusing the insulating bonding layer featured by the item (v) noted aboveis diagrammatically illustrated in FIG. 10 by way of example. In theembodiment of the metal-clad laminated board shown in FIG. 10, the bothsurfaces of the carbon-base substrate 51 are respectively coated withthe insulating bonding layer 52 constituted by the primer layer 52 a andthe bonding layer 52 b and the metal foil layer 53 in order. Thus, therequired electric wiring board can be produced.

In forming the insulating bonding layer noted in the items (i) to (v),the bonding layer in the items (i), (ii), (iv) and (v) and the polyimidelayer having the bonding ability in the item (iii) may contain properamounts of the granulated filler serving as a spacer. As the aforesaidfiller serving as the spacer, there may be used, for example, silica,spherical alumina and hollow balloons.

In the process of forming the insulating bonding layer noted in the item(i) to (v), insulating woven or nonwoven fabric may be embedded in thebonding layer noted in the items (i), (ii), (iv) and (v) and thepolyimide layer serving as the bonding agent noted in the item (iii)according to demand. This construction is illustrated in FIG. 11. In themetal-clad laminated board of FIG. 11, the insulating bonding layer 62comprising the undercoat 62 a such as of the polyimide coating membraneand the bonding layer 62 b enclosing the nonwoven fabric 62 c and themetal foil 63 are bonded to the both surfaces of the carbon-basesubstrate 61. Thus, the woven or nonwoven fabric embedded in the bondinglayer serves as a spacer to sufficiently separate the carbon-basesubstrate from the metal foil or lead frame, consequently to improve theinsulation breakdown properties of the electric wiring board by thethickness of the woven or nonwoven fabric.

As the woven or nonwoven fabric as described above, there may beselectively used electrical insulating and heat-resistant fabric such asfabric of synthetic fiber, natural fiber, glass fiber and so on. To beconcrete, there may be suitably used nonwoven fabric of aramid fibersuch as META-ARAMID PAPER (trade name of DuPont Teijin Advanced PapersLtd.) When the woven or nonwoven fabric applied therefore is too thick,the heat conductivity of the electric wiring board is degraded, andinversely, when it is too thin, the elastic insulation between the metalfoil or lead frame and the carbon-base substrate cannot be secured.Accordingly, the thickness of the fabric should be determined takingthese circumstances into account. To be concrete, it is appropriate todetermine the thickness of the fabric in the order of 30 to 150 μm, butthis should not be understood as being limited thereto.

Formation of the insulating bonding layer from the undercoat of thepolyimide coating membrane and the bonding layer is filed in order toproduce the electric wiring board containing the woven or nonwovenfabric by the following steps. Namely, the insulating bonding layer isformed by the steps of (a) forming the undercoat such as the polyimidecoating membrane on the carbon-base substrate, (b) laying the woven ornonwoven fabric impregnated with the bonding agent by applying thebonding agent to the fabric or immersing the fabric in the bondingagent, (c) laying the metal foil or lead frame thereon. Thus, therequired electric wiring board can be produced. As another method, thebonding agent is applied to the undercoat in the aforementioned step(b), and then, the woven or nonwoven fabric is laid thereon and coatedwith the bonding layer. In this case, it is required to apply asufficient amount of bonding agent onto the woven or nonwoven fabric soas to embed the fabric in the bonding agent layer (i.e. so as not toexpose the fabric), taking shrinkage of the hardened bonding agent intoconsideration. Further, the insulating bonding layer formed of thepolyamide layer serving as the bonding agent can be formed on theelectric wiring board in the same manner as the steps (a) to (c) exceptfor the process of forming the undercoat on the carbon-base substrate.In a case of using the film type thermoplastic polyimide bonding agent,the electric wiring board may be produced by placing the woven ornonwoven fabric between the two film type polyimide bonding agents,laying the metal foil or lead frame thereon, and then, melting andhardening the bonding agent. It is a matter of course that the woven ornonwoven fabric at that time requires high heat resistance to endureheat at a temperature higher than the melting temperature of the filmtype bonding agent. Incidentally, in placing the metal foil or leadframe on the carbon-base substrate, it is desirable to press theselayers by using a roll press, platen press or the like in order toclosely unite the layers without remaining air in between the layers.

The aforesaid metal-clad laminated board in the electric wiring boardaccording to the invention may be produced by a common method such as aconventionally known photolithography technology, thereby to suitablyform the electric wiring board having a printed wiring pattern asrequired. The electric wiring board thus obtained is applicable forvarious purposes in electric or electronic apparatuses. When the leadframe laminated board is demanded, it can be suitably used as it is forthe electric or electronic apparatuses. The electric wiring boardaccording to the present invention is excellent in heat conductivity andheat radiating property. Thus, the printed wiring board derived from themetal-clad laminated electric wiring board or the lead frame typelaminated electric wiring board according to the present invention canbe specifically applied for an electric circuit such as of electric orelectronic apparatus which generates heat in operation.

Although the embodiments of the present invention will be described indetail hereinafter in comparison with comparative examples, theinvention is by no means limited thereto.

Embodiment 1

A CC (trade name of Sentan Zairyo) of a carbon fiber reinforcedcomposite (hereinafter, referred to as “C/C composite”) of 3 mmthickness, in which carbon fibers are oriented in the thicknessdirection of a carbon matrix, was used as the carbon-base substrate. Theplate-like C/C composite is coated on its one surface with electrodeposition polyimide coating by an electrode position coating method on 30volts for 2.5 minutes at room temperature, dried at 80° C. for 10minutes, and then, baked at 250° C. for 30 minutes. Consequently, thewiring board with the electrode position polyimide coating layer wasformed on the carbon-base substrate. Further, a copper foil coated withsilicone bonding agent—KE1800T (trade name of Shin-Etsu Silicones Co.Ltd.)—was laid on the aforesaid electrode position polyimide coatinglayer so as to bring the bonding agent coated surface into contact withaforesaid electrode position polyimide coating layer. Prior to theapplication of the bonding agent to the carbon-base substrate, PRIMER-A(trade name of Dow-Corning Toray Silicone Co. Ltd.) was preliminarilyapplied to the surface of the copper foil with a brush in a primerapplying process. Subsequently, the laminated board thus obtained waspressed at 294N/cm² for 3 minutes by a heat press to remove air andsurplus bonding agent, and then, after releasing the pressure exertedthereon, subjected to heating treatment at 120° C. for 60 minutes toharden the bonding agent. Thus, the copper-clad laminated board wasprepared. The thickness of the electrodeposition polyimide coatingmembrane of the copper-clad laminated board was 20 μm, and the thicknessof the bonding agent layer was 100 μm, adding up to 3.19 mm in wholethickness.

Embodiment 2

A polyimide coating membrane was laid on one surface of a plate-like C/Ccomposite having 3 mm thickness same as that used in Embodiment 1 notedabove by applying polyimide coating material of RIKACOAT PN-20 (tradename of New Japan Chemical Co. Ltd.) with a brush. The polyimide coatingmembrane was overlaid with a copper foil of 70 μm thickness coated withsilicone bonding agent, i.e. KE1800T (trade name of Sbin-Etsu SiliconesCo. Ltd.) so as to bring the bonding coating surface into contact withthe afore noted polyimide coating membrane. Before applying thepolyimide coating membrane and bonding agent, PRIMER-A (trade name ofDow-Corning Toray Silicone Co. Ltd.) was preliminarily applied to thecopper foil with a brush in a primer applying process. Subsequently, thelaminated board thus obtained was pressed at 294N/cm² for 3 minutes by aheat press to remove air and surplus bonding agent, and then, afterreleasing the pressure exerted thereon, subjected to heating treatmentat 120° C. for 60 minutes to harden the bonding agent. Thus, thecopper-clad laminated board was prepared. The thickness of theelectrodeposition polyimide coating membrane of the copper-cladlaminated board was 20 μm, and the thickness of the bonding agent layerwas 100 μm.

Embodiment 3

A polyimide coating membrane was laid on one surface of a plate-like C/Ccomposite having 3 mm thickness same as that used in Embodiment 1 notedabove by plating the both surfaces of the plate-like C/C composite withnickel by an electroless plating method and placing, on the nickel-cladlayer, a copper foil of 70 μm thickness coated with silicone bondingagent, i.e. KE1800T (trade name of Shin-Etsu Silicones Co. Ltd.) so asto bring the bonding coating surface into contact with the afore notedpolyimide coating membrane. Before forming the nickel-dad layer andbonding agent, PRIMER-A (trade name of Dow-Corning Toray Silicone Co.Ltd.) was preliminarily applied to the copper foil with a brush in aprimer applying process. Subsequently, the laminated board thus obtainedwas pressed at 294N/cm² for 3 minutes by a heat press to remove air andsurplus bonding agent, and then, after releasing the pressure exertedthereon, subjected to heating treatment at 120° C. for 60 minutes toharden the bonding agent. Thus, the copper-clad laminated board wasprepared. The thickness of the nickel-clad layer of the copper-cladlaminated board was 20 μm, and the thickness of the bonding agent layerwas 100 μm.

Embodiment 4

Onto one surface of a plate-like C/C composite having 3 mm thicknesssame as that used in Embodiment 1 noted above, PRIMER-X (trade name ofDow-Corning Toray Silicone Co. Ltd ) was applied with a brush and driedat room temperature, to form a primer layer. On the primer layer, afilm-like silicone elastomer bonding agent, SOTEFA-70 (trade name ofDow-Corning Toray Silicone Co. Ltd.), and a copper foil of 70 μmthickness were overlaid in order. The laminate board thus obtained waspressed at 294N/cm² by a heat press and subjected to heating treatmentat 130° C. for 30 minutes to harden the bonding agent, consequently toprepare the copper-clad laminated board. The thickness of the primerlayer on the copper-clad laminated board was 1 μm, and the thickness ofthe bonding agent layer was 100 μm.

Embodiment 5

A plate-like C/C composite having 3 mm thickness same as that used inEmbodiment 1 noted above was dipped in silicon-containing polymer, i.e.HEATLESS GLASS GA-4(N) (trade name of Homer Technology Co. Ltd) atreduced pressure of 70 mmHg to permit the HEATLESS GLASS to plug finepores in the aforesaid plate-like C/C composite, and thereafter, allowedto stand for 50 minutes at room temperature. Subsequently, it was heatedat 120° C. for 60 minutes to harden the HEATLESS GLASS. Consequently,the plate-like C/C composite impregnated with HEATLESS GLASS wasprepared. Thus, the copper-clad laminated board was obtained in the sameway as that of Embodiment 1, except that the plate-like C/C compositeimpregnated with HEATLESS GLASS was used as the carbon-base substrate inthis embodiment.

Embodiment 6

As the carbon-base substrate, MB-18 (trade name of Mebius AT, as whichC/C composite base having carbon fibers oriented in first order isdesignated) was used instead of the plate-like C/C composite used inEmbodiment 1 and treated to prepare a copper-clad laminated board in thesame way as that in Embodiment 1. The thickness of the electrodepositionpolyimide coating membrane in the copper-clad laminated board was 100μm, and the total thickness of the board was 3.19 mm. Thereafter, thecopper-clad laminated board was etched to remove the copper foiltherefrom. The laminated board (3.12 mm in thickness) thus obtained isplaced on an aluminum plate (25 mm in thickness) and measured in itsheat conductivity by using a heat conduction meter QTM-500 (made byKyoto Electronics Co. Ltd.). Because measurement of heat conductionrequires a some degree of thickness of a measuring object, the aluminumplate was supplementarily used in this measurement. On measurement, thethickness thereof was 22.64 (W/m·K).

Comparative Example 1

As a comparative sample, a printed circuit board No. 31 (1.6 mm inthickness) produced by Sunhayato Corporation was used. This printedcircuit board is formed by coating the both surfaces of an epoxy/glassboard with copper foils.

The printed circuit board was etched to remove the copper foil from thesurface thereof to obtain an epoxy/glass substrate. The epoxy/glasssubstrate thus obtained is placed on an aluminum plate (25 mm inthickness) and measured in its heat conductivity by using a heatconduction meter QTM-500 (made by Kyoto Electronics Co. Ltd.). Becausemeasurement of heat conduction requires a some degree of thickness of ameasuring object, the aluminum plate was supplementarily used in thismeasurement in the same manner as Embodiment 6 noted above. Onmeasurement, the thickness thereof was 0.552 (W/m·K).

In carrying out the measurement, two of the substrates were piled to be3.2 mm in thickness in total far the purpose of making the thickness ofthe measuring object in the comparative example 1 equal to that inEmbodiment 6 described above. Further, in order to ensure the insulationproperty of the measuring object, the surface of the insulatedsubstrate, from which the copper foil is removed, was overlaid with awrap file (10 μm in thickness) by way of precaution. Incidentally,although the epoxy/glass substrate need not take such a measure forensuring the insulation property because it is intact an insulator, theepoxy/glass substrate to be measured experimentally was wrapped with thewrap film to maintain all the measuring condition.

It was found from the result of the measurement that the board accordingto Embodiment 6 of the invention is remarkably improved in its heatconductivity, that is, the board of the invention, which has heatconductivity of 22.64 (W/m·K), is considerably higher than the substrateof the comparative example, which has heat conductivity of 0.552(W/m·K).

The metal-clad laminated board for the printed wiring board according tothe present invention comprises the strongly united carbon-basesubstrate and metal foil and excels in various characteristics such asvolume resistance, surface resistance, and relative dielectric constant,dielectric loss tangent. These excellent characteristics of the printedwiring board of the invention satisfies the standard values of theconventional metal-clad circuit boards of this type. Thus, the printedwiring board of the invention could be effectively applied for therequired purposes. The devices used in the measurements described aboveare shown in Table 1, and the measuring results are shown in Table 2.

TABLE 1 Test Item Testing Device Maker Model Name Remarks InsulationResistance Insulation Resistance Hewlett Packeard Co. HP4329A HIGHRESISTANCE METER Amplifier Surface Resistance Measuring Device YokokawaHewlett YHP 16008 RESISTIVIT CELL Electrode Volume Resistance PackeardCo. Dielectric Constant Dielectric Constant Hewlett Packeard Co. HP4194AINPEDANCE GAIN-PHASE Measuring Dielectric Loss Tangent Measuring DeviceANALYZER Device HP4194A MEASURMENT UNIT Units HP1645B DIELECTRIC TESTFIXTURE Electrode Breakdown Strength High-voltage Breakdown KikusuiElectronics TOS 8700 WITHSTANDING VOLTAGE Measured Up DielectricStrength Measuring Device Corporation TESTER to 10 kV Heat ConductivityHeat Conductivity Kyoto Electronics QTM-500 Measuring Device Corporation

TABLE 2 Item Treating Conditions Embodiment 6 Comparative Example 1Value in JIS Code Remarks Volume Resistance (Ω · cm) C-96/20/65^(*1)4.60 × 10¹⁴ 1 × 10¹³˜1 × 10¹⁴ 1 × 10¹² JIS C6481 Surface Resistance(Ω)C-96/20/65 3.58 × 10¹² 1 × 10¹¹˜1 × 10¹² 1 × 10¹¹ JIS C6481 RelativeDieletric Constant C-96/20/65 2.1 4.1˜4.6 Below 5.5 JIS C6481 (1 MHz)Dielelectric Loss Tangent C-96/20/65 0.005 0.03˜0.04 Below 0.045 JISC6481 (1 MHz) Breakdown Strength^(*5) (kV) C-96/20/65 (6 = 0.11 mm) 8.2— — JIS K6911 Peeling Strength (N/cm) A^(*2) 92.4 18.6˜23.5 Over 10.8(over 1.1 kgf/cm) JIS C6481 E-1/150^(*3) 12.7 9.8˜11.8 Over 15.7 (over1.6 kgf/cm) JIS C6481 After soldering^(*4) 18.8 18.6˜23.5 Over 15.7(over 1.6 kgf/cm) JIS C6481 Heat Resistance Solder^(*4) O.K O.K No bulgeand break acceptable JIS C6481 200° C., 60 min. O.K O.K No bulge andbreak acceptable JIS C6481 Heat Conductivity (W/m · K) 22.64 0.552 — JISR2618 ^(*1)In air of constant temperature and constant humidity at 20°C. and 65% RH for 96 hours) ^(*2)Normal State ^(*3)In air of constanttemperature at 150° C. for 1 hour ^(*4)At 260° C. for 20 seconds^(*5)Continuous Pressor Testing

Embodiment 7

As an alternative to the copper foil used in Embodiment 1 describedabove, a lead frame formed by punching a copper plate of 500 μmthickness was used. The other conditions for producing a lead framelaminated board for this embodiment were common to Embodiment 1. Thelead frame laminated board resultantly obtained was processed in thesame manner as that in Embodiment 6, that is, etched to remove the leadframe being a substitute for the copper foil in the former embodiments.The board having no lead frame was measured in heat conductivity. It wasfound from the result of the measurement that the board of thisembodiment is remarkably higher in heat conductivity than that ofEmbodiment 1, similarly to the board of Embodiment 6.

Embodiment 8

Onto one surface of a plate-like C/C composite having 3 mm thicknesssame as that used in Embodiment 1 noted above, UPIREX-S (trade name ofUbe Industries, Ltd., as which polyimide varnish is designated) wasapplied with a brush, and then, UPITITE (trade name of Ube Industries,Ltd.) of 20 μm thickness, which is a film type polyimide bonding agent,was placed. Further, the composite was overlaid with a copper foil of 70μm thickness, pressed at 170° C. for 30 minutes at the pressure of294N/cm², consequently to obtain the copper-clad laminated board. Thecopper-clad board thus obtained was measure in heat conductivity in thesame manner as Embodiment 6. It was found from the result of themeasurement that the copper-clad board produced in this embodiment hashigh heat conductivity, similarly to that obtained in the foregoingembodiments. On conducting a peeling test defined by JIS C6481, theboard produced in this embodiment exhibited as high as 1.2 kgf/cm inpeeling strength.

Embodiment 9

Onto one surface of a plate-like C/C composite having 3 mm thicknesssame as that used in Embodiment 1 noted above, a copper foil of 70 μmthickness was applied through UPITITE (Products No. UPA-N111: trade nameof Ube Industries, Ltd.) of 20 μm thickness, which is a film typepolyimide bonding agent, and pressed at 250° C. for 3 minutes at50N/cm², to obtain a copper-clad laminated board. The copper-clad boardthus obtained was measure in heat conductivity in the same manner asEmbodiment 6. It was found from the result of the measurement that thecopper-clad board produced in this embodiment has high heatconductivity. On conducting a peeling test defined by JIS C6481, theboard produced in this embodiment exhibited as high as 1.1 kgf/cm inpeeling strength.

Embodiment 10

As an alternative to the electrodeposition polyimide coating membraneused in Embodiment 1 described above, a polyimide-vaporized polymerlayer formed in a vacuum was used. The other conditions for producing acopper-clad laminated board for this embodiment were common toEmbodiment 1. The thickness of the polyimide-vaporized polymer layer onthe copper-clad laminated board obtained in this embodiment was 20 μm.Upon removing the copper foil from the board, the measurement of heatconductivity was carried out in the same manner as Embodiment 6. It wasfound from the result of the measurement that the board of thisembodiment is remarkably higher in heat conductivity than that ofEmbodiment 1, similarly to the board of Embodiment 6.

Embodiment 11

A polyimide coating membrane was formed on one surface of a platelikeC/C composite having 3 mm thickness same as that used in Embodiment 1noted above by applying polyimide coating material of RIKACOAT PN-20(trade name of New Japan Chemical Co. Ltd.) with a brush and baked at200° C. for 30 minutes, thereby to form a polyimide coating membrane of20 μm thickness. The polyimide coating membrane thus formed was overlaidwith metal-aramid paper of 120 μm thickness impregnated with siliconebonding agent, i.e. KE1800T (trade name of Shin-Etsu Silicones Co. Ltd.)and further overlaid with a copper foil of 70 μm thickness. Beforeapplying the polyimide coating membrane and bonding agent, PRIMER-A(trade name of Dow-Corning Toray Silicone Co. Ltd) was preliminarilyapplied to the copper foil with a brush in a primer applying process.Subsequently, the laminated board thus obtained was pressed at 294N/cm²for 3 minutes by a heat press to remove air and surplus bonding agent,and then, after releasing the pressure exerted thereon, subjected toheating treatment at 120° C. for 60 minutes to harden the bonding agent.Thus, the copper-clad laminated board was prepared Thereafter, uponremoving the copper foil from the board, the measurement of heatconductivity was carried out in the same manner as Embodiment 6. It wasfound from the result of the measurement that the board of thisembodiment is remarkably higher in heat conductivity than that ofEmbodiment 1, similarly to the board of Embodiment 6. On conducting anelectrical breakdown test defined by JIS K6911, the board produced inthis embodiment exhibited as high as 10.8 kV in breakdown strength.

INDUSTRIAL APPLICABILITY:

According to the present invention, there is provided a printed wringboard capable of dissipating heat and superior in thermal conduction,which is formed in a metal-clad or lead frame lamination. The printedwiring board according to the invention has the carbon-base substrateand metal foil or lead frame united firmly therewith.

The printed wiring board can be produced at a low cost because the rawmaterial of the carbon-base substrate is inexpensive. The printed wiringboard is light because of a light the carbon-base substrate, so thatelectric or electronic apparatuses using the printed wiring board can belightened.

What is claimed is:
 1. A printed wiring board comprising: a carbon-basesubstrate which comprises carbonaceous material impregnated with aninorganic coating agent or metal so as to fill up pores in saidcarbon-base substrate, at least one insulating bonding layer of apolyimide coating membrane on said carbon-base substrate and a bondingagent layer on said polyimide coating membrane, and a metal foil or leadframe on said at least one insulating bonding layer.
 2. A printed wiringboard set forth in claim 1, comprising said metal foil, said carbon-basesubstrate and said insulating bonding layer to form a metal-cladlaminated board.
 3. A printed wiring board set forth in claim 1,comprising said lead frame, said carbon-base substrate and saidinsulating bonding layer to form a lead frame laminated board.
 4. Aprinted wiring board set forth in claim 1, wherein said polyimidecoating membrane is an electrodeposition polyimide coating membrane. 5.A printed wiring board set forth in claim 1, wherein an insulating wovenor nonwoven fabric is embedded in said bonding agent layer.
 6. A printedwiring board set forth in claim 2, wherein an insulating woven ornonwoven fabric is embedded in said bonding agent layer.
 7. A printedwiring board set forth in claim 3, wherein an insulating woven ornonwoven fabric is embedded in said bonding agent layer.
 8. A printedwiring board set forth in claim 4, wherein an insulating woven ornonwoven fabric is embedded in said bonding agent layer.
 9. A printedwiring board set forth in claim 1, wherein said bonding agent layercontains filler serving as a spacer.
 10. A printed wiring board setforth in claim 2, wherein said bonding agent layer contains fillerserving as a spacer.
 11. A printed wiring board set forth in claim 3,wherein said bonding agent layer contains filler serving as a spacer.12. A printed wiring board set forth in claim 4, wherein said bondingagent layer contains filler serving as a spacer.